Iowa has recently made silencers legal and I have two on order, one for .22 rimfires and one for centerfires up to .30 cal. I’ve got questions. Will a 7MM STW with a silencer be significantly louder than a 7 x 57 with a silencer? How about a small cartridge like a .17 Hornet? Also, I’ve thought about getting a rifle in .300 BLK for use with subsonic loads. I assume the subsonic loads with the 230 to 250 grain bullets are full pressure loads. What about reduced subsonic loads with 100 to 150 grain cast lead bullets for varmints like raccoons or coyotes? Would they be accurate and make less noise when used with a silencer?

The higher the pressure, the louder the noise. But it is the pressure at the muzzle which is key. A longer barrel means less pressure and temperature for the silencer to deal with. The 7mm STW is rated for 65k, the 7mm Mauser only 51k psi. A larger powder charge will make the noise duration longer and seem to be louder.

The small 17 caliber bullets have a tiny sonic boom. The difference between the 17 Fireball (26 grain charge) and the 17 HMR (much smaller charge) muzzle blast is significant as the larger powder charge of the center fire cartridge is much louder when suppressed or unsuppressed.

A full pressure load with a 125 grain bullet in the 300 blk will be about 21-22 grains, the subsonic loads of any bullet weight will be less than 10 grains depending on the powder used. The muzzle blast is much less with the subsonic loads so I would assume that they are no where near max loaded.

I've used cast bullets of 225-230 grains which were ok (2 moa at best) but nothing lighter. 147 fmj had the worst accuracy of any load I tried, 6 moa.

The difference in powder charges (and noise levels) for subsonic loads varies little according to bullet weight. For varmits, pick the most accurate load.